1. Field of the Invention
The present invention relates to a method of controlling an automatic clutch which is controlled in operation depending on the engine rotational speed, vehicle speed, etc., of a motor vehicle such as an automobile, and more particularly to a method of controlling an automatic clutch upon quick deceleration of the motor vehicle as when it is abruptly braked.
2. Description of the Prior Art
There are known automatic clutches employed in automatic transmissions, continuously variable transmissions, or the like. For example, Japanese laid-open patent publication No. 60-8553 discloses an automatic clutch in an automatic transmission, and Japanese laid-open patent publications Nos. 62-238132 and 1-105062 show automatic clutches in continuously variable transmissions.
The automatic clutch is engaged when movement of the motor vehicle is to be started, and disengaged when the motor vehicle is to be decelerated to a stop. If the automatic clutch were not disengaged until after the motor vehicle is completely stopped, then the engine would stall. Usually, therefore, the clutch is disengaged when the speed of the motor vehicle becomes lower than a predetermined speed.
There are instances where, while the motor vehicle is running, the driver is required to abruptly apply the brake to stop motor vehicle. Since the automatic clutch is usually disengaged when the vehicle speed decreases to a predetermined speed, the engine may be stalled because the disengagement of the clutch is slow.
In the automatic transmission disclosed in Japanese laid-open patent publication No. 60-8553 and the continuously variable transmission disclosed in Japanese laid-open patent publication No. 1-105062, if the deceleration of the motor vehicle is of a predetermined level or higher, then the clutch is disengaged to prevent the engine from stalling even when the vehicle speed is higher than a predetermined speed.
In the continuously variable transmission disclosed in Japanese laid-open patent publication No. 1-105062, if the deceleration of the motor vehicle is judged as a predetermined quick deceleration, then the predetermined speed, i.e., the vehicle speed below which the automatic clutch is disengaged, is set to a high-speed level for disengaging the automatic clutch early, thereby preventing the engine from stalling.
However, when the motor vehicle is so abruptly braked (e.g., a so-called panic brake is applied) that the road wheels are locked, since the rotational speed of the road wheels decreases to zero very rapidly, it is difficult to prevent the engine from stalling even with the conventional control processes disclosed in the above publications. Specifically, according to the conventional control processes, the clutch is disengaged if the deceleration of the motor vehicle is of a predetermined level or higher when the motor vehicle is quickly decelerated. Actually, however, in the case of a panic brake, the speed of the motor vehicle has already been decelerated to a certain level when the deceleration reaches the predetermined level. Starting to disengage the automatic clutch upon arrival of the deceleration at the predetermined level may be too late, thereby resulting in an engine stall.